Cerium, with atomic number 58 and an atomic weight of 140, is a relatively abundant rare-earth lanthanoid. It tends to be found in mineral ores containing other rare-earth elements used in photonics applications, such as neodymium and ytterbium. In recent years, rare-earth ore production around the world has diminished to such an extent that it is almost entirely reliant on Chinese supply. Now that China has restricted exports, the prices of rare-earth elements have soared. Credit: Images of Elements.com.